1. Field of the Invention
This invention relates to control apparatus for vehicles with differential speed steering and particularly control apparatus for track laying vehicles having differential speed steering with a continuously adjustable hydrostatic drive unit on each side of the vehicle with output shafts of both drive units connected with a signal transmitter that detects turning movement and signals a speed regulator whose output is connected to two valving stages, each one connected to one of the drive units through a summing element to which a set point is fed for travel speed by a set point adjuster.
2. Description of the Prior Art
In devices of this type known to date a tacho-generator was connected with each drive unit output shaft. A speed-dependent signal is transmitted from the tacho-generator to a regulator for the differential speed, in which case this regulator compares the two signals and processes them and then sends an output signal to the valve end stages, through which the hydraulic control-pressure valves are influenced, each of which acts on the adjusting device of a hydrostatic drive unit. These devices have the shortcoming that a regulation intervenes only if a differential speed occurs, i.e., different paths are traversed during the same time period, that is, a curve is inadvertently described. Only after a curve segment of varying size is traversed, depending on the inertia of the regulating device, straight-run control, which is to be achieved with the said device, becomes active. Due to the curved or cornering movement, the vehicle is then travelling in an undesirable direction and consequently the direction of travel must be corrected, arbitrarily by the driver.
Vehicle drives with a hydrostatic drive unit without the aforementioned regulator were the basic structures for such vehicles (DE-PS 25 11 176) and corresponding U.S. Pat. No. 4,076,090. Such drives have the disadvantage that it is difficult for the driver and requires continuous steering correction in order to steer the vehicle precisely straight forward. In contrast, an improvement is achieved by the prior art device described above as soon as the regulator for differential speed becomes active. However, this improvement is less than sufficient, since the straight forward behavior in such devices is erratic and must be corrected by the operator as described above.